Emroyonic vertebrate heart development is a process that can be easily adapted to an analysis of directerd cell migration and the possibvle role of extracellular matrix materials. The embryo is histologically very simple at these early stages of development, i.e. there are only three germ layers. The critical stages for investigating directed cell migration are HH Stages 5-8 (19-26 hrs of incubation). The precardiac cells can be readily identified as a cluster of cells between the ectoderm and endoderm. The primary emphasis of this study will be to study cross-coronal-, and frontal-sections, we will investigate the role of ECM components in directional movements. The molecules to be analyzed include: hyaluronic acid and sulfated glycosaminoglycans, collagens, fibronectin (cell-associated), vinculin, laminin, actin, and basement membrane-proteoglycan. Most of these studies will be carried out using monospecific polyclonal antibodies. These immunohistological studies will be accompanied by scanning and transmission electronmicroscopy. These correlative studies should give useful information with regard to the factors involved in directed cell migration.